1. Field of the Invention
This invention relates to a fiber-forming random polyamide consisting of recurring units of the formulas: ##STR1## wherein R is a C.sub.3 to C.sub.10 alkylene and wherein from 30 to 40% of the units are 6IA units and from 2-15% of the units are 6RA units. These polyamides can be prepared and shaped into fibers by conventional melt polymerization and melt extrusion techniques.
2. Description of the Prior Art
U.S. Pat. No. 4,022,756 describes a batch process for preparing fibers of a polyamide consisting essentially of recurring 6TA and 6IA units in a mole ratio of between 50:50 and 80:20, respectively. In carrying out the process, an aqueous solution of an appropriate mixture of hexamethylene diammonium terephthalate (6TA salt) and hexamethylene diammonium isophthalate (6IA salt) is heated in a suitable vessel (e.g. autoclave) under conditions of controlled time, temperature and pressure to provide molten polymer (referred to herein as 6TA/6IA). Then, the molten 6TA/6IA is extruded directly from the base of the autoclave into fibers which are heat treated in the manner described in U.S. Pat. No. 4,022,756. The heat treated 6TA/6IA fibers are dimensionally stable and are characterized in having a relatively high moduli (e.g. 80-110 gpd) and the dye performance and adhesion-to-rubber characteristics of nylon 66. The 6TA/6IA fibers are particularly useful in carpet, wrinkle-resistant apparel fabrics and reinforcing structures such as tire cord.
One difficulty encountered in extruding 6TA/6IA (particularly 6TA/6IA consisting of 60 mole % or more 6TA) into fiber by the batch process described in U.S. Pat. No. 4,022,756 is that a small amount of 6TA/6IA remains as a shell on the inner wall and agitator of the autoclave after extrusion. Unfortunately, the 6TA/6IA shell, unlike a nylon 66 shell, does not entirely melt during the next polymerization. Particles of the 6TA/6IA shell disperse in the molten 6TA/6IA formed in the next polymerization to yield heterogeneous 6TA/6IA, a condition referred to herein as "polymer heterogeneity". Attempts to provide useful fibers by melt extrusion (melt spinning) of heterogeneous 6TA/6IA has not been entirely successful. In those instances where fibers are obtained, the fibers contain opaque particles of noticeable size, and generally have unacceptable properties. Therefore, high quality fibers can be obtained only by cleaning the autoclave between each run (i.e. polymerization and extrusion) to remove the 6TA/ 6IA shell that remains therein after extrusion. Cleaning of the autoclave is time consuming and costly and, therefore, is not feasible for commercial operations.
Accordingly, it is an object of the present invention to provide a modified fiber-forming 6TA/6IA which can be extruded into fibers by a batch process without encountering polymer heterogeneity and without cleaning the extrusion vessel between successive runs to remove the polymer shell therefrom.
Another object of the invention is to provide a modified 6TA/6IA fiber which has properties, such as modulus and boiling water shrinkage, comparable to the 6TA/6IA fiber described in U.S. Pat. No. 4,022,756.